Tiltman's parents were from Scotland, though he was born in
London. He joined the British Army in 1914, and saw service at the
front during the Great War with the King's Own Scottish
Borderers. He was wounded in France, and won the Military Cross
for bravery. He was seconded to MI1
shortly before it merged with Room 40.

From 1921–1929, he was a cryptanalyst with the Indian Army at
Army Headquarters, Simla. They were reading Russian diplomatic
cypher traffic from Moscow to Kabul, Afghanistan and Tashkent,
Turkestan. In the small section of five or less he was involved in
all aspects, directing interception and traffic analysis as well as
working on cyphers; he said he was exceptionally lucky to have this
experience in other branches of Signals Intelligence.

After a decade as a War Office civilian at GC&CS, the
interwar cryptographic organization, John was recalled to active
service. His experience enabled him to assist in many areas of
endeavour at GC&CS. He was considered one of Bletchley Park’s
finest cryptanalysts on non-machine systems.

John Tiltman was an early and persistent advocate of British
cooperation with the United States in cryptology. His advocacy
helped achieve smooth relations during World War II.

In 1944, he was promoted to Brigadier and appointed Deputy
Director of GC&CS. He continued in 1946, as Assistant Director
of the Government Communications Headquarters (GCHQ), successor to
GC&CS. John Tiltman became Senior GCHQ Liaison Officer at the
Army Security Agency in 1949. He retired as a Brigadier.

After reaching normal retirement age, he was retained by GCHQ
from 1954–1964. From 1964–1980 he was a consultant and researcher
at the NSA,
spending in all 60 years at the cutting edge of SIGINT.

John Tiltman made the transition from the manual ciphers of the
early 20th century to the sophisticated machine systems of the
latter half of the century; he was one of a very few who were able
to do so. "The Brig" as he was affectionately known in both
countries, compiled a lengthy record of high achievement.

On 1 September 2004, Tiltman was inducted into the NSA's "hall of
honor", the first non-US citizen to be recognised in that way. The
NSA commented, "His efforts at training and his attention to all
the many facets that make up cryptology inspired the best in all
who encountered him."